1. Field of the Invention
The present invention relates to a method and an apparatus for processing a time code used for an editing operation involving converting picture information of a predetermined system into that of another system.
2. Description of the Related Art
For broadcasting or producing a video software package of picture information originally imaged on cinema film for release to the public in a theater, the picture information is frequently converted into a standard video signal of an NTSC (National Television System Committee) system or a
(Phase Alternating by Line) system.
For this purpose, a system arranged to use a telecine apparatus serving as a picture scanning device has been considered. Such a device is illustrated in FIG. 1. As an example, the following description will be directed to the conversion of picture information captured on cinema film into a video signal of the NTSC system.
Normally, cinema film 1 is imaged at a rate of 24 frames per second. To obtain a video signal of the NTSC system, that is, a video signal having 525 scan lines and field frequency of 59.94 Hz, the telecine apparatus 2 operates to reproduce the picture information imaged on the cinema film 1 at a rate of 24 frames per second (precisely, 24/1.001=23.97602398), which is the same as the imaging speed. Then, a field frequency converting unit 3 operates to perform a so-called 3:2 pull-down process.
As shown in FIG.2, the so-called 3:2 pull-down process is a process that is executed to perform interlaced scanning of the cinema film for converting an even field of the film into an even field of a video signal and an odd field of the film into an odd field of the video signal. Since one frame of the cinema film is composed of two of the same fields with no time lag, the field frequency converting unit 3 operates to output the video signal of the NTSC system without any unfavorable time lag. Four frames on the input side are converted into one frame on the output side. Since no undesirable arrangement of the field order inside of the frame takes place, an observer feels no unnatural reproduction of the picture.
When reproducing a still frame video signal of the NTSC system in the fashion described above, the reproduced picture can be created in an undesirable fashion because the picture of a field of a given frame of the video signal is different from the picture of its adjacent field of the same frame unless a reproducing start point is properly selected.
In FIG. 2, when setting a reproducing start point to the 02 frame (F) of the video signal, the 02 frame of the video signal is produced from fields of the 01 frame and 02 frame of the cinema film. Between the two fields a time lag exists. As a result, an observer senses an unnatural reproduction of the still frame video signal. Accordingly, it is desirable to provide a system overcoming these prior art shortcomings.